Build date 1/99, why some lift kits say after 3/99

[makey98]

I have a 99 f-250 with build date of 1/99 so I have going under the assumption that it is a late 99 even though it has the lumbar support.

Some suspension kits and other parts say they will work before build date of 3/1/99. What happened in this time period? What other issues can I look for?
Thanks all.

[107stroker]

trac bar bolt size and u bolts in front were different.

[dereku]

See whar kind of turbo you have thats a dead giveaway to the early or late

[immortalic]

Didn't some of the earlier late 99's have the early 99 suspension differences? Like a sort of hybrid between the two?