I need to identify workers working in the same firm and same MSA. I have panel data.

Y=a + b*X + firm*MSA fixed effects (1)

Y=a + b*X + firm_it + MSA_it (2)

The first specification uses time-invariant two-way firm*MSA fixed effects.

The second specification uses time-variant firm (firm_it) and time-variant MSA (MSA_it) fixed effects. Can you *please* tell me which specification identifies workers working in the same firm and same MSA correctly?