Each new SEC is attached to an Event where that SEC can be earned / won by participation in the event(s)
either a single event to take part in, or a combination of different events to fill a reward bar.
When there is a reward Bar, the bar is Filled based on the number of credits used on the events.
The total number of credits used to fill the bar varies for the different events, but past events have shown it to be between 1500 to 2500 credits used to fill the bar.
Also, in the process you may win back credits, which can then be used, So your Total number of Credits from your 'credit store' May be much less than the full amount needed, because you won back credits.
I have had a few events, where I won back more credits than I used from my credit store, so I ended up with a Net Gain.
Each event and experience will be different so you have to best judge your own credit usage.
If you miss the event or the SEC award, then past SEC cards are a Random reward on some of the events.
Depending on how many Past SEC cards you Don't own, the random SEC rewarded may Not give you the SEC you want.
Some events also give out a Joker card as one of the awards.
Jokers can be used to get Past SEC cards, so with a joker, you get to choose which of the past SEC cards you want to use it on.
And as Mentioned above, Owning DOLZ NFT cards generate a daily reward of BabyDOLZ that can then be spent in the BabyDOLZ store. One of the Items available is a Joker card.