The 8th day of tabernacles does not have to fall on sunday-------it could fall on any day of the week because it occurs on the 22nd of the 7th month-------Jesus was born during this feast----on the 1st day of the feast, Mary gave birth to Him--------and on the eighth day of this feast, He was circumsized-----it could have fallen on a sunday during that year but that is irrelevant because it could also fall on any day of the week and still be sacred-------The feast days that MUST fall on Sundays are Wavesheaf and Pentecost because the instruction says to celebrate them "on the morrow after the Sabbath"---------which is the same as the day after Saturday.
 

In Christ,
Granny Priscilla.