Sam2 (and benignuman): Your quote from the gemoro kesubos (17A) is slightly erroneous- R”shmuel bar nachmeni in the name of R’jonasan says it is MUTTAR to look in a kallahs face, etc…but the gemoro says that the halocho is not like him.
However ,from this gemoro itself ,you clearly see that the kallahs did NOT cover their faces! Hence, you COULD look at their faces! if the minhag was to cover their faces, the gemoro’s statement would make no sense!
Furthermore- earlier in the sugya, the machlokes of bais hillel and bais shammai concern the statement-“_Keitzad merakdim lifnei hakallah”, but it is pretty clear that they both agreed that one looked at the kallah to see how she looked.
The answer to this contradiction is probably benignuman’s answer- R’Jonasan’s statement maintains “lehistakel”-meaning intently and this is what the gemoro refutes. Bais Hillel and Bais Shammai talk about looking casually. (see Bais shammai’s statement about “chiger and sumoh”)