The difference in A+ for 18 vs 19 is that, theoretically, they can have the exact same skills since A+ essentially tells you that it is in on the higher side of 5 ball of the star rating. Star rating of 5 balls just means over $3700 starting salary(or that's what the guide still has at least). You would have to see the skills of both to know if the 19 was worth having without the year of training, or if an 18 would surpass where the 19 is.
I would prefer the A- 5/5 as opposed to the A+ 5/4 since you're guaranteed a higher potential with good starting skills and can profit more if you sell, or have more room to train if you keep.
I once had a team with 1757 players and was $25,835,360 in debt. This is not that team. Join the Discord group open to anyone, but especially for USA managers to improve your club or get involved with the U21 and NT programs
(https://discord.gg/cKpNkt2).