TheBaldingModel,
First of all, I am not sure by guarantee, if you mean that, will you be sure that the surgeon has guaranteed a transplant of 2200 grafts(which involves a count) or if the guarantee is that there will be a definite GROWTH of 2200 grafts. There is a difference.
After excision of a donor strip during FUT the harvest might be actually larger than 2200 grafts.
However, at Norwood 4A, you should receive 4000 grafts, total. Generally speaking, one multiplies the level of hairloss on the Norwood scale by a factor of 1000 to gain an approximation of the no. of grafts necessary to create the illusion of density. The 2200 grafts probably just accounts for the reconstruction of the hairline and the densification of the top half to two-thirds.
Latinlotus is right. The survival rate of grafts is 70% to 90% and diminishes in subsequent HT surgeries.
Hope this helps, and as always, I am open to criticism from the experts.