i am 100% sure the numbers are rounded.
what we see is a rounded number with zero decimal places (rounded to the nearest integer i am pretty sure)
but what the attributes actually appear to be is a numnber with at least one decimal place.
if you make careful note at the biginning of the season, you will notice some guys gain +1 here or there that are still showing +0 on the growth.
what is happening is you have a guy at 70.3 SPD (shows as 70), he has +0.3 growth in SPD (shows as +0) but his behind-the-scenes number is now 70.6 (shows as 71, even though his spd improvement still shows +0)
now wehther the game SPD plays as 70.6 or 71 I am not sure, but there is definately rounding of the attributes, i am positive of it.
as far as the 1.5 games sample size, 2 things:
1) i think all player growth happens 1-hr after the game ends, so you would see growth at halftime
2) thats way to small a sample size to judge anyway. and there seems to be some sort of odd-eve cycle to player growth, that is you tend to grow more after game 2 than you did after game 1, more after game 4 than you did after game 3, etc (incrementally by game of course).
and rememebr you should be playing your freshman in 2 preseason games, so by the end of the 2nd game of the regular season you should have 4 games of growth.