A TICK indicates that this prayer or action still remains. If there is a X this indicates that either the rubrics do not allow it or the rubrics no longer require this as either omitted in the Missal or changed in the instructions.
Where there is a TICK/X, this indicates it was optional, so the priest could do either.
So, e.g. The Canon is said silently, being the sole prayer of the priest as intercessory for the faithful, thus said in silent reverence. This is up until 1964, when it could be said in a loud voice. Then in 1967 was said aloud.
As another example Solemn Mass with deacon only was NOT permitted up till 1964 then was permitted from 1964 onwards
This list is not complete. There are more like for example where it require the server to ring a bell if there are communicants instead of the long standing Confiteor.
Communion of the faithful during Mass is a separate action and rite, not essential to the Mass in itself. Please note that the Confiteor (I confess) was omitted from the 1960 changes, even though the Ritual Romanum of 1960 still has the Confiteor as part of the rite of Communion outside of Mass, and for Communion of the Sick and Viaticum.