I´m not saying I know the truth. But, looking on my own dials, I´d state that original/untouched dials don´t have this "unusually coarse, vertical grain" but in most cases "standing" numerals in the counters and a smother radium lume - as seen on one of my pics in comparison. The lume on the discussed dial looks like my watchmaker would have applied it - as well as he can. Furthermore the Longines signature is bigger as I would expect it on an early 13ZN dial. No open 6/flat 3s ? Maybe, but here we have an accumulation of dubious ingredients...
rgds - h.u.
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