I too have read somewhere (Greener?) that the more elaborate Damascus patterns can be less cohesive and more-brittle (less-strong). The examples described being some of the more elaborate Belgium-sourced patterns that were produced just before the turn of the last Century. Arguably, you could overwork the metal in the process of using 4 or more fagots (the proper English term for the hammer-welded metal laminate bars that were used) to produce a barrel. (I have, however, seen some English 4 iron nitro-proved Crolle tubes that were absolutely spectacular to behold! I'd lose very little sleep over the subject if ever I owned and shot one.)
I am relieved to hear that you and I read the 1891 proof-house test results the same way. My current (well, Circa 1894) Damascus shooter is barreled with best English 3 Iron Laminate. Not as pretty as some of the Crolles, but arguably a bit tougher. Since it is a 20 (which are famous for somewhat higher pressures than 12s) I'm not too-unhappy about the less-artistic appearance.