votum is a very strong term, meaning closer to "vow" than "desire" (a term deliberately chosen to water it down). You can't "vow" to receive the Sacrament without believing in and intending explicitly to receive it. It's not enough to "vaguely desire" it somehow.
I haven't been following this thread and long ago concluded this topic produces very little discussion that is genuinely profitable, but is anyone actually positing the idea that a "vague desire" suffices? Somehow I doubt it. A vague desire for "a snack" or "a vacation" isn't even sufficient, so why would anyone pretend it suffices in more serious matters?
Desire seems clear enough, as does any distinction between an explicit desire and a vague one. At the end of the day, God is either limited by/reliant upon water -- which He Himself creates and maintains in existence -- in order to communicate the graces that He creates, or He is free to do as He judges to be appropriate in any particular situation.
St. John the Baptist, among others, was justified/sanctified in the womb. How did that happen, unless God did/does as He knows is best, regardless of His own laws, whether of nature or grace?