how to track duplicate values?

I have a duty roaster with 11 sheets which are locations where the assigned person goes to either day or night among those 11 locations but the roaster updates frequently and it's from location to assigned shifts change all the time.

for example if a person was assigned D on 13/2 in location A

but now he is assigned

N on 12/2 in location B (another sheet)

how can i track duplicate values so i can remove the previous entry in the same date(could be in different sheets)

the sheet lay out

Name. Shift. 13/2. 14/2. 15/2

Alina. Day. D

Sal. Day. D

.

.

.

Saim. Night. N

Alina. Noght. N

.

.

.

Location sheet. LocationB sheet. LocationC.