[DigitalJack]

This is just a phonetic misspelling of the contraction "should've" which really is pronounced "should of"

[jjuel]

However, should've is a shortened version of should have so I think the point still stands.

[colejohnson66]

Ain't the English language great when we can have multiple contractions such as "couldn't've"

[mirimir]

Or "should a" ;)