May I know why the author of the following sentence used "remembering" instead of "...if I remember (it) rightly..."?. (Isn't 'remember' a stative verb?)
"The Gem and the Magnet, if I'm remembering rightly, started about 1905."
It is, but we can and do use stative verbs in the progressive form sometimes. Here it serves to show that the person is tentative and unsure about the memory (to me). He or she is almost asking to be corrected if wrong.