If you have (at least) two oriented edges, it's always impossible to deduce PLL from only the top face.
Case (i) zero or two twisted corners: You can swap the two oriented edges and the two oriented corners.
Case (ii) four twisted corners: By pigeonhole principle, two of the corners will have the same up-facing sticker; swap those two and the two oriented edges.
Case (iii) three twisted corners: For every S CLL case, there's a corresponding AS CLL case with the same U colours and the opposite permutation parity, and vice versa. Change the corners accordingly and swap the two oriented edges. (Example:
S vs
AS.)
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So that leaves only the dot OLLs. For the sake of brevity, I'll use the same numbering as Roux's CMLL numbers (but with our usual letters for OCLL names).
S/AS: Always possible to deduce.
O: Always impossible to deduce (do an H perm).
H/pi: The cases with only two distinct U colours on the corners (H1, H6, pi3, pi5) can always be converted to an identical looking case with an E perm or H perm. The rest are always possible to deduce: two corners will have the same U sticker, so the identities of the remaining two corners are fixed; since we know permutation parity, we can also identify the two corners with the same U sticker.
T/U/L: The cases with two identical U colours on the twisted corners (L2, L3, U2, U6, T1, T4) are always impossible to deduce (do an E perm or H perm). The cases with two opposite U colours on the twisted corners (L4, L5, U1, U4, T2, T6) are always impossible to deduce (wlog the colours are red and orange; swap the two red corners and the two orange corners and twist accordingly). The remaining cases are always possible to deduce: the identities of the two twisted corners are uniquely determined and permutation parity lets you identify the two oriented corners.
tl;dr summary: If you can see all four edges and two adjacent colours on the twisted corners, then you can deduce the 1LLL. Otherwise, you can't.