I hadn't considered that in nearly as much depth as you did, John. You are prefectly right - Said would not have been in a position to be one of the signatories so early on. He would just have been "one of the apprenctices", busily learning. He would not have been involved with something as complicated as a chalice!
The "Bell-shaped" chalice bowls are all Harris period, as you said, so the pawmark is most likely to be that of Dobson, (which was where I was leaning. His mark often does have that spikey sort of E shape at the beginning.
Although it is a bit odd that Dobson's signature would be on a piece which was made by Harris and V. Boffo, maybe it was during a period when they were trying out putting an "artist's mark" on pieces to see if they sold better? I think that did happen, probably around the same time as Rosenthal was being designed for the American market, and the artist's mark was required. (for example, most Japanese Globes have a Michael Harris signature on them)
There is one other signature found on some bits of Mdina - I have 2 examples, both on pieces that were post-Harris though.