The "M30" reference in 1901 does suggest that this birth was registered late (M30 = Mar 1930, the quarter when the late registration took place), and the reason may have been that they were getting things in order before the marriage.
There may be a baptism record. It isn't necessarily online, and it could have taken place anywhere up to right before the marriage. There's no easy way for us to say.
If you search for "Margaret V Hughes" (using her mother's maiden name, there is both a possible original record for a Margaret Victoria b. Mar quarter 1901 and registered in West Derby district, as well as a cross-reference for Margaret V. Hughes "m1930" (e.g. March 1930 late registration).
There is as second child, Edith M Hughes, who similarly was registered in 1930 but was born in 1902 - similarly there is "Edith M Hughes" reference in 1902 cross-referencing 1930, and a separate Edith May Hughes reference in the same quarter in Toxeth Park district.
I can also see a possible marriage for some parents in 1915 (William Ritson/Margaret Hughes), which would suggest the following scenario to me:
William and Margaret have a long-term relationship as common law husband and wife with several kids. For whatever reason (one or the other had a previous marriage, the first child came along before they got married and then it was easier to just pretend they were), they don't marry until 1915, but the kids are raised as Ritson. However, at least Margaret and Edith have birth certificates that say they are "Hughes" and don't name their father.
Fast-forward to 1930. Although William and Margaret are now husband and wife, the two eldest daughters still are listed as "Hughes". Therefore, they apply to change these records. The births are re-registered under Hughes/Ritson in Liverpool district (which in the meantime has absorbed the West Derby and Toxeth Park districts where the births were originally registered).
This leaves a bunch of records which aren't clearly linked:
The original "Hughes" births in West Derby/Toxeth Park.
Hughes/Ritson births in Liverpool district in 1901/1902 which point to the 1930 registrations
The actual 1930 registrations.
