I readily agree that parsing the Vincentian canon is a bear.
Indeed it is. Thank God that it is much easier to understand His will for us! There is only one Great Commandment:
Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. – Matthew 22:37-38
If we don't get that one right, no matter how hard we try to be doctrinally correct - all else is loss:
Unto the angel of the church of Ephesus write; These things saith he that holdeth the seven stars in his right hand, who walketh in the midst of the seven golden candlesticks; I know thy works, and thy labour, and thy patience, and how thou canst not bear them which are evil: and thou hast tried them which say they are apostles, and are not, and hast found them liars: And hast borne, and hast patience, and for my name's sake hast laboured, and hast not fainted. Nevertheless I have [somewhat] against thee, because thou hast left thy first love.
Remember therefore from whence thou art fallen, and repent, and do the first works; or else I will come unto thee quickly, and will remove thy candlestick out of his place, except thou repent. – Revelation 2:1-5
Moreover, once we get the one and only Great Commandment in its proper place and priority in our spirits, souls and minds - then we must turn to the second commandment. Because if we keep them both, then we are assured that we are in the heart of the law and the prophets.
Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second [is] like unto it, Thou shalt love thy neighbour as thyself.
On these two commandments hang all the law and the prophets. – Matthew 22:37-40
The rest of what we do is just "details" - and concerning the likes of the Vincentian canon et al - we ought to be very careful about choosing our theological battles lest we become an obstruction to Christ.
Then were there brought unto him little children, that he should put [his] hands on them, and pray: and the disciples rebuked them. But Jesus said, Suffer little children, and forbid them not, to come unto me: for of such is the kingdom of heaven. And he laid [his] hands on them, and departed thence. - Matthew 19:13-15
Little children come in all ages.
And I, brethren, could not speak unto you as unto spiritual, but as unto carnal, [even] as unto babes in Christ. I have fed you with milk, and not with meat: for hitherto ye were not able [to bear it], neither yet now are ye able. For ye are yet carnal: for whereas [there is] among you envying, and strife, and divisions, are ye not carnal, and walk as men? For while one saith, I am of Paul; and another, I [am] of Apollos; are ye not carnal? Who then is Paul, and who [is] Apollos, but ministers by whom ye believed, even as the Lord gave to every man? I have planted, Apollos watered; but God gave the increase.
So then neither is he that planteth any thing, neither he that watereth; but God that giveth the increase. – I Corinthians 3:1-7
To God be the glory!