What do you mean after 3 is an urban myth? I would book my 3 FP+ in the first 3.5ish hours of the day, then spend the next 8ish hours making more and more. I can search through my posting history, but I definitely spelled out some impressive FP+ days back in 2019.
Never remember the Pre-fastpass days (I'm too young for that), but did go for 4 days between FP+ and G+ starting (October 2021) so that's my standby only experience (It was the worst Disney experience I can remember, still fun but frustrating).
As far as legacy FP, I was 19 in 2013 when it shut down and went quite a bit in middle school/high school. I don't know exactly how many trips I went on between 1999 and 2013, but we did go for 10 days straight around 2010ish I remember running to RNRC, Soarin, and TSMM at rope drop with everyone's tickets and telling them to meet me somewhere else. Then watching times and running across the park to somewhere else, only to run back and meet them somewhere multiple times a day. My mom hated splitting up the group. I much prefer it being all digital (FP+/G+). I also remember being mad at my older sister because she didn't want to get up early and we didn't get FP until everyone was tapped in.
My dad even went one morning to go to Soarin at rope drop to get us FP (he was up anyway and we were at beach club). Then he learned everyone had to tap in before it would issue FP, so he had 1 and no one else did.
So no, I don't remember pre 1999 standby only, just 2021 standby only. I also don't remember early legacy fastpass, just late legacy FP.