How common are preterite forms in -A in Bokmål?

While the two major liberal Norwegian newspapers (Dagsavisen and Dagbladet) are permissive when it comes to embracing -a definite forms of (most) female gender nouns, they are restrictive when it comes to past simple forms of verbs of the first group (which can be both -et, and -a, according to official school grammars). Dagsavisen does not tolerate -a forms except for some verbs like kaste ''throw'' (kasta 18% vs kastet 82%), lukte ''smell'' (lukta 36% vs luktet 64% ), jobbe ''work'' (jobba 10%, jobbet 90%), love ''promise, praise'' (lova 23% vs lovet 77%) and ønske ''wish, desire'' (ønska 17% vs ønsket 83%). Dagbladet tolerates -a forms of a few more verbs (in addition to the ones just mentioned):  hoppe ''hop'' (hoppa 12% vs hoppet 88%), flytte ''move'' (flytta 19% vs flyttet 81%), hente 'bring, fetch'' (henta 11% vs hentet 89%), koste ''cost, sweep'' (kosta 11%, kostet 89%) and ''danse'' (dansa 19% vs danset 81%). So, in a formal text, you should better stick with -et forms and avoid -a forms altogether. In a semi-formal text, you may add forms of aforementioned verbs (especially kasta would look nice). In an informal text (and in informal speech), you can use the -a ending with any verb of the 1st group, but you don't have to, if you don't feel like doing it. If it's too complicated for you, you can use kasta, lukta, jobba and hoppa in both writing and speech, and -et for all other verbs of the 1st group (in both writing and speech). Remember that both -a and -et forms are correct, according to Språkrådet