Scribe 2 of 𝓟 originally wrote the nonstandard reflexive form themself, which he immediately corrected by erasure to themselves. This scribe wrote themself in three other places in 𝓟:
In each of these three other cases, scribe 2’s f was only partially written, then overwritten with the v and followed inline by the es. Thus these three corrections were also immediate. According to the Oxford English Dictionary, “in standard English themself was the normal form to about 1540, but disappeared about 1570” (see under themselves in the OED). The form themself is found in today’s colloquial speech, especially in generic uses (as in “someone hurt themself ”), but none of the four manuscript examples of themself are generic. It appears that scribe 2 of 𝓟 was simply used to writing self rather than selves (as in the singular forms myself, thyself, himself, herself, itself, and yourself ), thus his tendency to accidentally start writing self for selves.
Summary: Maintain the standard reflexive form themselves instead of themself throughout the text; scribe 2 of 𝓟 tended to write themself as a scribal slip.