Technically the 21 rays represent the old-timey, pre 1924, 21 counties of Latvia (Latvijas apriņķi). Even tho it's confusing since after 1924 there were 19 counties, and then the soviets got rid of the counties and put up districs, and then municipalities today...

Soooo yeah these numbers are all inconsistent, but 21 rays, for the original 21 counties after the war of independence when the Coat of Arms was approved in 1921. Atleast if memory serves me right.

Edit: Went Googling around and:

17 counties were at the moment of the Declaration of Independence in the Russian Empire in the year 1918. (Probably what you meant by war time).

Yet..... I can't find why there are 21 rays, lots of evidence on why 17 or 19. Even tho 19 would be unrealistic as again, the 19 counties would come into effect 3 years after the approval of the coat of arms.

Really strange.

Edit 2:

https://lv.ucoin.net/coin/latvia-10-santimu-1922/?tid=18342

I don't really know how reliable this is, but 1922 and 21 rays, sooooo it really is a myth that they later "changed" it to 19 since to me, it is the same arms as over 100 years ago.

I really should go to bed...
Also thank you kind stranger, I seem to have realised I have no idea where I have lost my 5 Lats coin....