3 or 4 I only ever did 5 with the same blade once.
I think there is something in what you say. I have taken a feather to 21 shaves and it is still shaving comfortably. I had some razor burn on the neck on shave #10 but I kept going in case it was my technique on the day. Sure enough that problem has not returned. Apart from good lather I think wetting the stubble well before shaving is the key. I also had 21 shaves out of Astra SS and Rapira blades.I used to be a 3 days and out guy. Bet then, I started just pitching the blade when it started to feel significantly dull, or tugged. Now, I routinely get 10+ shaves - often more than this. I use Feathers almost exclusively. My beard is not terribly fast growing, but it is pretty rough. It's a sandpaper sort of feel after 24 hours. The key to extending blade life is a good hot rinse, keeping the blade dry (blow it off after use), and using a shallow blade angle. Steep angles wear out blades very quickly due to forces being applied perpendicular to the edge, rather than parallel to it, resulting in scraping the hair, instead of cutting it straight on.
This is so odd that I just noticed today.
My usual routine was to open the DE part way, rinse it off and set it down awaiting the next shave.
Following that procedure I would get 2-3 shaves per blade.
I use the Gillette Bleue Extra.
Well just this past week, I had forgotten to open it up and rinse it out and so far I have gotten 6 shaves off of it.
That's an amazing number for me and maybe it's just this blade, but I for sure am going to try it again.
I would like someone else to give it a try and see how it works out.