Lendl being officially credited with 'only' 94 titles including 42 indoors (obviously though still an insane number) is one of the most misleading stats around in terms of players that exclusively played in the open era, when he clearly won many more than that. His body of work at unsanctioned events was pretty unrivalled, so he is an even bigger victim of having an understated title count than Connors or McEnroe.
Ignoring all 4 man invitational events, I previously counted at least 30 additional titles that he won, in which he had to play in 4 or 5 matches (and my list is likely to be incomplete as well), 17 of which were indoors.
Of course it goes without saying that 'ranking points' is not a factor in terms of what should count and what shouldn't, with the Masters / YEC not awarding any ranking points before 1990 (and it was still a more highly regarded tournament then than it has been in recent times), the WCT Finals and WCT events also not counting for ATP rankings etc.
The ECC in Antwerp (which Lendl won 5 times) looked to be a more highly regarded tournament in the 80s when it was an unofficial invitational tournament, than it was in the 90s after 1991 when it was an official ATP tournament. The Toronto Indoor event at Maple Leaf Gardens was a bigger deal when it was an invitational tournament from 1981-1984 (Lendl won it twice during that period), than when it was an 'official' grand prix / ATP tour event in the mid-80s / 1990 (when Lendl won it again). Of course there was a big difference between a proper invitational tournament (many of which had packed crowds, great fields and more prize money on offer than most / many official tour events) and a hit and giggle exhibition.