Not sure how the older Catalina models were put together, the late 70’s and 80’s the top and bottom hulls are bolted together. Some of the other boat mfg glued the hulls together and then stapled them till the glue set.
A friend just redid a Starwind 19 in which it was glued and stapled because the foredeck was lifting from the hull like shown. I did not see marks like that on the inside but, these look like deteriorating staples rather than bolts.