I did struggle to understand why "se recordaba" was in the singular in "... solo se recordaba a los difuntos el 1 de noviembre" [= "the deceased were only remembered on November 1st"].
At first, I was tempted to make it plural to agree with "difuntos". As a passive construction, I thought it could be compared with "se venden apartamentos de lujo en la playa" - (given as one of the examples in Forming the Spanish passive with se (la pasiva refleja) ... which is the lesson we get referred to).
Anyway, I was also "scratching my head" regarding the use or non-use of the "personal 'a' " in a passive sentence of this nature - [Compare "Se buscan secretarias con experiencia" in that^ same lesson] ..
I then looked in my grammar book [by Butt and Benjamin], and discovered that this is part of a construction which evolved comparatively recently in the Spanish language - in which the use of the "personal 'a' " makes a singular verb necessary even when the [passive] subject is in the plural.