Here's what I'd hazard a guess on the 264, 270, 272, 299, etc. would be that they were devoid of an Lindner Quality Control Stamp for whatever reason, in production, got hungup @ the engraver, etc. & that the Lindner Quality Control Stamp of a Crown over HAL were applied in April 1893 or later.

Cheers,

Raimey
rse