Issues with End date in Service request

Hello Experts.

we create service request based on categorization selection, end date/resolution date will be captured by system automatically

but when we generate report ,there are certain default cases/service request found end date/Resolution date captured incorrect(it is just 5-7 service request out of 2000)

i checked Transaction log but no records for change in date found for that service request , and i have no clue but iam convincing user that ,End user may be changed the date before hitting save button.

i tested the same scenario but is it is working fine.

i suggested user that we should grey out Date field in Service request so that no user is allowed to change.

but still is there any possible way to check to find out the exact cause

please let us know

Chinna