Blanketed drivel.
2013:
This was pretty much a full season and a great one at that. Missing the Aussie Open but still going 75-7 with 10 titles and 2 slams should more than makes up for it

Nadal skipped World Group 1st Rd. vs Canada on
Indoor HC that was held from Feb 1-3. Played Vina Del Mar (Clay 250) that began on Feb 4. LOL and made the final. Ok, you'll say he was recovering from the back injury in 2012 yada yada right?

Spain slips into Relegation Playoff that Nadal shows up for of course since it's Madrid Clay. Stomps the ever living hell out of Stakhovsky 6-0 6-0 6-4..... 2013
FAIL because it was a full season for the most part and DC was not truly missed due to injury.
2014:
I'm going to give him 2014 even though I have some doubts. It was the back, then the wrist, then appendicitis, then stem cell therapy lol. Regardless, he had his reasons that year at every turn. It wasn't meant for him to play after Wimbledon it seemed. Btw, I'm not laughing at the injuries. It was just the way they unfolded at the time. 2014
PASS
2015:
A recovery year of sorts with patchy play. True that he was healthy and played a full season as you mentioned. Spain was in big trouble at this point in DC after a miserable 2013-14 (some of it unnecessarily). Nadal did well in Stuttgart, claimed the title, but fell short in Queens to Dolgo in the 1st round obviously wanting matches since he was playing both warm ups. Wouldn't you agree? Wimbledon is a disaster as Dustin Brown pulls off the upset over Nadal in the 2nd rd. Nadal takes a straight month off before playing and winning Hamburg (Clay of course). The week before that, which was three weeks after Wimbledon, Spain desperately needed Nadal vs Russia with only Robredo and Andujar basically. Maybe it was a case of underestimating Russia or maybe not. I can't recall now, but he could've shown up to help them dig out of the hole. Especially being healthy with 3 weeks rest and knowing Spain could use him. Btw that was Indoor HC
. Later on he finally stepped up to play on Indoor HC vs powerhouse Denmark who hasn't been in the World Group for nearly 25 years. He faced Mikael Torpegaard, a journeyman with a career high ranking of #170 which he just achieved this year in 2019. Has never made it out of qualifying rounds at slams. Won a couple challengers. Nadal thumped the guy for his first Indoor HC DC match/win since 2011 when he defeated Olivier Rochus lol. Now, 2016 will be spent trying to make it back to World Group. I have to go with FAIL here because of that.
2016:
Skips Zone Group vs Romania who offers up an inspired Copil as their Top Gun. Lopez holds him off and RBA/PCB handle the other no names after Lopez & Co. gift the doubles match away. Easy Indoor HC win. A missed chance for Nadal to make it appear that he tried to play something besides clay at DC. Normally, this would be that chance. Sadly, Nadal injured his wrist at RG along with Federer (knee) shortly thereafter and sent the tennis world into Darkness for a few months. I genuinely felt sorry for Nadal. Even more sad after Federer went down at Wimbledon. Could it be over for both of them? Bad times for a little while there. Anyhow, Nadal showed up to play doubles vs India later in the year. You know it's gravy when Marc Lopez plays singles and Nadal plays doubles with a 5-0 score. Nadal could have just stayed home, but a HC win even in doubles is better than nothing I guess. Hang with the boys and celebrate returning to the World Group. A positive moment for Spain, but since Nadal made no difference at all in the outcome of these matches it must be ruled a FAIL. Easy matches yes, but in the ghetto all year thanks to Rafa.
2017:
New life 
Nadal is back from the dead at AO. All is well in Nadal World again with the exception of Federer NEO BH raining down on the Bull. He is ready for anyone, anywhere, anytime, except for Federer
. Moving on to the point now...2017 DC had a good and easy start with Croatia. Nadal didn't show up which is understandable right after the AO. Spain handled business anyhow. Next up was Serbia which falls between Miami and Monte Carlo. Yes, it was possible to send guys there in an attempt to win, but Spain elected not to. DC captain left Nadal out as it would interrupt his clay schedule. I understood the move at the time with Federer winning #18 and spanking the field. Djokoray were vulnerable too. Nadal needed the French Open badly to keep pace. Spain sent the B team to Belgrade. Indoor HC btw lol. Excusable this time. Nadal is a slick fella. As far as his 2017 season, it was a full season. 78 matches played, all Slams played, all Masters played, 2 Slams won, 6 titles. So, 2017 was a full season for Nadal and Spain maintained the World Group without his help, but not because he was injured or didn't play a full season. He pursued personal goals instead of team goals. Spain settled so Rafa could chase Roger. Rafa again was liable for DC lull. Despite my understanding of his endeavor, I have to say FAIL from a DC point of view. Also you were wrong again about his availability and full seasons. Not to be a know it all 
2018:
Playing the British on clay LMAO, stay home Rafa and heal the hip.Too soon. Germany was coming up in 3 months and almost exactly 3 months later Nadal decided he wanted to play tennis again lol. DC on Clay was his moment to shine and help bring the trophy back home to Spain possibly.He might as well since every time he wins a slam, Roger does too. Two birds, one stone. Clay Prep & DC to wipe away 3 months of HC avoidance. After going on to fully recover and have yet another great clay season, Nadal also plays his best Wimbledon in years making the SF. After that he wins Canada Masters and is a favorite to win UO. Unfortunately, Nadal retired with a knee injury vs Delpo in the UO SF. He would not make be able to make the DC SF vs France that was only a few days away. This year will PASS because I give Nadal the benefit of the doubt injury wise with it being a Slam SF. I will remind everyone once more that this was Indoor HC. Man, that guy is good

After that he had two more injuries and a surgery without playing a match. Scheduled an ankle surgery that no one earth knew about that took place on ATP Finals draw day LOL, but listed abdominable injury as the reason for withdrawing

. Point being that it appeared Nadal avoided Indoor HC after DC. It's the most obvious thing that the tennis world has ever known if they choose to know it. DC is only one example of his selectiveness. Not hating here, but putting things into perspective. Have a good day.