Yep that sure does look like "13"

.
The entrance in Abe Exoddus would have been a underground one (maybe the one that Sam's held in, cos' the concept pics of them looks like it would be very
deep underground).
It does make sense that of the possbility of more then 1 Vykkers lab on Mudos, otherwise they would be too easy to wipe out the Vykkers crazy experiments and product lines...