The difference is plating of contact area, RoHS and reinforced lock.
DF1B-**P-2.5*** : Tin, non RoHS, discontinued
DF1B-**P-2.5***(01) : 0.2 μ gold, RoHS2
DF1B-**P-2.5***(28) : 0.2 μ gold, RoHS2, reinforced lock(discontinued)
Replacement of DF1B-**P-2.5*** is DF1BZ-**P-2.5*** that is tin plated contact and complies with RoHS2.