They will surely have to use 2018/19 credits, given that they've said they're doing that for the home games, stating that the 2019/20 season was 'incomplete' in terms of ticket sales.
There is though, the group that reached the 13 home credits last season for the first time, that are fighting for the right to be included in the sales for the home games, so whatever the outcome of that is, the club will probably be consistent and do the same with the aways.
It's not going to make very much difference though, as the same people will have kept up their credits. Your 14 from 2018/19, would probably be equal to your 12 from 2019/20 anyway, in terms of what games you would qualify for, however they do it.
As you say, there will likely to be more availability lower down the pecking order, with there being no need to buy, to retain credits.