The POG 90 might have been a little tougher than something like the Red Head or the PDP Open(for which the string was 'designed', I believe). The idea behind the string pattern was to string all the mains and a half-dozen or so of the bottom crosses with the 22' section, finishing the crosses with the 11' piece. This necessarily put a 'tie-off' in the middle of the crosses...not something most stringers want to try. With the PG 90 pattern, you would have a long end of the mains looping down to the appropriate cross and string up to the top tie-off. Then, start the rest of the crosses in the 'middle' and finish the crosses per normal. Getting the proper tension on that 'middle' cross was the trick.
The reason for the 22' lengths was simple ease of production. It was easier to QC a shorter length of nat gut and 22/11 worked on the early 'conventional' sized rackets.
There was at least one string supplier(70s into the 80s) who shipped their NYLON strings in 22' coils...Winn, I believe. The idea was the 22' coil could be cut to mate with two other 22' coils for two 'full' sets.
These youngsters have it SOOOOO easy these days