As a crochet designer I vary rarely see or use anyone else's patterns mostly just to keep my mind clear and untainted from other designs and focus on my own.
I recently found a vintage amigurumi pattern that looked (at first glance) similar to one of the base patterns I have for a group of my patterns.
I figured I would look over the pattern just to be sure the differences were more than just visual. YES, they were!
First thing I noticed was the largest stitch number in the rounds of the body was 36, wow that is way smaller than the picture presents it to be.
Second thing I noticed was that the approx. finished size at 39 rnds was listed at 8 inches tall with a G (4.00mm) hook. I am thinking how in the world is that possible??
Almost all of my patterns are done with a G hook so I am very familiar with the finished sizes I make with it, which is usually around 6 inches. The patterns of mine that I am referencing to go up to 47 rnds and 48 sts around. Now the stitches around don't really matter in this scenario but I am letting you know anyway.
By now you are thinking it has to be the yarn. The pattern says it used Red Heart Super Saver yarns, same as me. Ahh but maybe a bit of the difference has to do with the fact that yarns in the 90's weren't exactly the same as they are now, they were tougher, thicker and coarser. So I am fine with giving it a little extra height to compensate for the difference, maybe an inch at the most.
Another thing to note is that the gauge size for the vintage pattern was 4 sts x 4 rnds = one inch. Most people hardly pay any attention to gauge when it comes to amigurumi because most of the time it is only important when using the appropriate size safety eyes. My patterns are typically 5 sts x 5 rnds = one inch. I would have to go up to a H or even an I sized hook to get the 4 x 4 gauge it called for. I decided against it because I hate seeing stuffing through my stitches.
Now, I am fully aware that I crochet very tightly because I very seldom have a tester come out with the same size as myself with having to drop several hook sizes. With knowing this I added 3 extra rnds to their pattern to make it a one piece heady and body vs having to sew it together. Even with this change the results were interesting.
The conclusion ...
Their G hook, red heart super saver medium weight yarn at 39 rnds = 8 inches.
My G hook, modern red heart super saver medium weight yarn at 42 rnds = 5.25 inches!!
Just another example that
1. yarns change over time and can skew the finished results.
2. even with the same material and hook size the results are going to be different because everyone has different tensions.
I hope this helps when you get a vintage pattern and it isn't coming out exactly right, don't get frustrated too much, there are other factors at play here.