This is valid in the three types of items (coins, banknotes or exonumia).
When we search only by territory/country and results are order by face value, ruling authority or type, an index in show at top of the results:

But if we use any filter more, the index is hidden (not always):

Can be show the index always (or in more cases)? If we filter a ruling authority and the results are order by the ruling authority, the index is not need, but in other cases it is need.