The reason the marked letters in and the sets of initals are crucial on identifying Sinaiticus, is because they verify and conclusively show that Simonides' words were right and that he wrote the Sinaiticus, making initals of manuscripts he used. The marked letters in folio 262 have little plus signs from the middle to the bottom of the first column and in the top of the second column. Consequently, the sets of initals also proves that Sinaiticus is not the oldest because Sinaiticus there are 63 initals so far that we discovered written, and Simonides stated he marked initals of manuscripts he used for "certain passages and readings":

"In various places I marked in the margin the initials of the different MSS. from which I had taken certain passages and readings."
(The Journal of Sacred Literature 1862-10: Vol 2 Iss 3, Page 250 Link)


63 initals are from Picture 1's 16 sets of initals (Link) + Picture 2's 15 sets of initals (Link) + Picture 3's sets of initals 10 sets of initals (Link) + Picture 4's 12 sets of initals (Link) + Picture 15's 10 sets of initals (Link) , showing that Simonides did write Sinaiticus in 1839 due to both Sinaiticus containing manuscript initals and Simonides mentioning he used initals for "different MSS [manuscripts]" he used.