Between roughly the mid-1960s and the late 1970s Dalí signed blank sheets in enormous quantity. Those sheets passed to publishers who printed images on them, some authorised and many not. The signature on such a sheet is genuinely Dalí's; the image on it may be nothing to do with him.
That makes the ordinary print checks insufficient. A pencil signature that sits on the paper's surface, an edition fraction in the right hand, good paper — all can be present on a print the artist never approved.
The standard reference for Dalí's authorised graphic work is Albert Field's catalogue. Matching an image against it establishes whether the artist authorised the edition at all, which is the question that actually matters here.
For prints of consequence, a specialist opinion is warranted and the trade expects it. The market prices unattributed Dalí prints as decoration, which is a rational response to the history.