There's nothing wrong with the winny ammo - many moons ago the ole corelockt bullet was killing animals just fine as yours is doing also. The "change" is expectation of the ammo, it's doing what it's always done, if your a behind the shoulder guy maybe you were a little low/high/back etc and your blood trail reflected that. Sounds like it all worked out just fine in the end - the blood didn't reach expectation. That probably happens more often than not.
If your expectation is they don't run, better shoot to anchor them high shoulder shots to break them down and that would require a well built bullet to knock out both shoulders and exit.
Congrats on a successful hunt, I think when it doesn't go down like we dreamed it up (i'm guilty of that myself) we start questioning things. Shot a doe the other day with a 150 grain partition out of a 270 weatherby mag at under 100 yards for meat didn't realize she was a slight quarter too hit shoulder on entry not on exit. She took off like she was hit, but she took off had me scratching my head. Took about 15 or so yards before i would pickup the blood trail she made it about 45-50 yards i could smell her well before i found her. It ended well just didn't live up to expectation - don't let expectations ruin the fun out of it.
Happy new year;