Stoke work and quality swims when muscles are fatigued?

Hi all. My question also ties in to swimming sets past point when stroke begins to deteriorate. I’m trying to get back in shape and am currently swimming 100s free on 1:35 as my challenge sets and upping the number. Usually doing them at 1:27-1:31. 6 is where I feel in command but 8 is just toughing it out and 10 might be possible if I didn’t die first. So my question is should I swim those last 2-4 for the lactate training? Or privilege keeping stroke intact and do less? As a returning member after long break here, I get this may have been discussed at length, so apologies if that is case. But my real question is the value of doing stroke emphasis work *after* the hard set. It makes sense to me, but I’m not sure if it does to anyone else, coaches, physiologists, etc. What I have begun to do is a 100 easy after the challenge set and then swimming 4x100s at same time I was holding (1:30ish), 50 easy and leaving again on 2:45 interval. I do these really focused on form, tightening core, lowering stroke count (from 14 to 13 for at least first 50) working tuns, etc. I think swimming a controlled “easy fast” stroke after muscles are fatigued must be of some value, but I only remember doing stroke and DPS type swimming early in workouts under a variety of coaches. But I’m 62 and haven’t had masters coach for 15+ years, so maybe thinking has changed? I guess the questions are ultimately if we ever train past point of stroke falling apart and how best to train once we’ve reached that state. Put another way, which approach to 10 100s (10 straight or 6+4) should predominate in any given period of training?