The order is Fancy Pants, Pocket Posey, Upper Crust.
It DOES sound like we haven't got any new info to go on, doesn't it? If nopony can remember the exact details, then how can the order be sorted out?
Well, the trick is to, as the puzzle's summary stated, treat the statements as non-superfluous - in other words, each statement MUST provide some useful information about the order. If they can't tell us anything then the solution you're thinking of is wrong. No ifs and no buts.
Let's talk about the first clause. In order for this statement to actually tell us anything, at least Upper Crust or Pocket Posey must have seen The Collector in a red hat, because otherwise the statement would be entirely worthless. Therefore, Fancy Pants can't be the third-chooser, as he must be followed by a pony who saw The Collector in a red hat.
Moving on to statement 2, if Upper Crust was in Canterlot's tallest tower 15 years ago, again, the statement would tell us nothing new, so she couldn't have been there. And if nopony lent The Collector an umbrella then the statement is superfluous. Therefore, somepony MUST have lent him an umbrella. But who?
If Fancy Pants were that pony, then he won't be coming first. We know from the first clue that he isn't last in line, so this would put him second. But if he IS second, that would render the third clue (the one about falling in love) useless, and make the puzzle unsolvable. So Fancy Pants never lent The Collector an umbrella.
Assuming both Upper Crust and Pocket Posey lent The Collector an umbrella, that would mean Fancy Pants would be first in the order, making the first statement superfluous. So one or the other lent an umbrella, but not both. Likewise, if Upper Crust and Pocket Posey both saw The Collector in a red hat, then Fancy Pants would be first, rendering the second clue superfluous. So one or the other saw The Collector in a red hat, but not both.
Now, let's assume the possibility that Upper Crust BOTH lent an umbrella and saw a red hat. From clue 1 we know she can't be first, which would render clue 2 superfluous. So if she did one thing, she cannot have done the other. The same logic applies for Pocket Posey: she must have done only one of those things.
In both cases, Fancy Pants would be first, and so, from the third clue, Upper Crust must have been the one to fall in love first, and so the final order is Fancy Pants, Pocket Posey and Upper Crust.