Los Angeles County, California, keeps a running total of the number of registered voters in each party, and the number of independents. Here is a link to that page.
Since registration closed for the June 3 primary on May 19, the number of registered voters has declined. Every qualified party has declined, except that the Libertarian Party has increased. The number of voters not registered in any qualified party has declined. Democrats have dropped 4,731; Republicans have dropped 3,980; American Independent has dropped 234; Americans Elect has dropped 28; Green has dropped 67; Peace & Freedom has dropped 20; the total of independent voters and voters registered in other parties has dropped 670.
Libertarian registration has gained 61.
The number of voters registered with nonqualified parties, including Independent increased by 6,482.
The number of No Party Preference voters (shown as Decline To State in Los Angeles) declined by 7,152.
I think that in certain cases where a permanent vote by mail ballot is returned, the voter may be purged. For example, if a forwarding address is in another county, they can check whether the voter has registered in that county.
LA has a very low share of PVBM (28%). In El Dorado County it is now 67%.