NO.
Partner DID NOT give aces, partner passed.
mick came close the first time. I read partner as defensively oriented...balanced, quite probably with a couple extra aces. He's playing the combination, tho: dealer may get stuck, opponents may not have 20 total or just barely enough to make the board...or, even if they have something like 30 meld, that our side will pull 31.
As a side note, if my team was 35 from a win (in range to coast out) and the opposition was 160 points from the finish line, I probably wouldn't make a 20-meld bid after first seat saved the Dealer. I suppose this makes me a non-aggressive player.
No, it makes you too afraid of the negative possibilities. I understand: you're worried that partner will have junk (or no trump suit), and you figure to save. But let the opponents name trump, and your chances to save drop considerably. If the score is 465-100, and if your hand is really weak (maybe 1 likely, and 1 uncertain ace...


say, for the uncertain ace)...then your position is justifiable because *you can't go set* with this score. If your hand's rather good AND balanced, I'd rather bid. Say you have:



















OK, it seems comfortable to pass and pull 20...but give declarer any 2-suiter and this hand falls apart.
Plus, you have tricks for partner. And look what has to happen...East opens 50 (say), you bid 52. For things to go wrong, West has to pass...then East has to pass whatever North does. There's considerable pressure on West, in particular, to bid...and quite a bit, even on East, if West passes. Give North







in ANY suit, with 1 other ace...your side will likely make. Can East risk that?
Finally, there's a significant difference between 465 and 480. 465 requires 20 meld, AND 20 trick points. At our 465-341, say the opponents take it cheap-ish and score 65 while shutting us out. They're at 406. We better get some meld...because if our side doesn't make the board, they don't have to throw the shutout at us. Now we're in trouble...it's double bidder out.
If we have 480, they have to throw the shutout...case closed. Granted, if I have 18+, I know they'll have to throw it. It's not safe to go overly passive, tho, without at least a 3-hand lead *before* double bidder out. Double bidder out means about 435+ for each side...and figure 'average hands' run about 65. So the score's got to be about 480-240 or so. If I'm at 465, I'd rather have a bit more cushion...maybe 465-210 so they need 3 pretty good hands, 2 of which are shutouts.
If it's at all close, tho...give the meld. Give information. Too many things have to be wrong for this to burn you, whereas passing fails any time partner has anything decent. Note, too: in this situation, passing lets the opponents buy the hand CHEAP. If you give 20, and partner can take the bidding to 65, you may be forcing the opponents too high, at 70...so even if they CAN throw the shutout, you still gain.
Thought of another way to put this. If you pass in this situation (up 465-341, East opens 50, you have 20 meld)...what you're doing is bidding your hand AND your partner's hand, in essence. You're bidding that he won't have much, when he can have *anything*.