Thank you for your reply, Ali.
The three slots I'd like to question are in the following set:
Half Crown, Victoria, 1839-1901, Circulation Issue, Including Varieties:
Slot No. 1: Halfcrown 1839, currency issue. This coin is extremely rare, rated R4 by ESC (only
11-20 examples believed to exist), even if very rarely available the purchase price
is prohibitive for even above average collector.
Slot No. 18: Halfcrown 1876/6. This is even not recognized variety at all, just re-punched numeral
as very common on most Victorian coins. This is not recognized in Spink, ESC, Bull or
Davies (most comprehensive catalogue of every known date,type and variety of British
silver coins since 1816). Not sure how/why this attribution was made, normally it's
quite challenging to achieve variety attribution even if the variety is in the books
mentioned above. Only one coin graded and most likely is destined to remain the only
one forever.
I believe that these two slots should be surely non-competitive, there is no chance that average collector will be ever able to complete this set and compete with these two slots being competitive.
Slot No. 17: Halfcrown 1876/5 This is rare but recognized variety. It's for consideration. At the moment again only one example is graded and in this case NGC normally refuses to make slot competitive (as happened to me with 6027677-026) but for some reason not in this case.
Thank you for consideration.