There is no way of knowing the odds in the past or now.
There are two ways. One would be to collect enough data to do a statistical analysis. The simpler way would be for Totem to publish the algorithm they use. I think Totem should do the latter.
I also would appreciate it if Totem published the odds of winning for all of the games. We can, however, go some way towards estimating the odds by analysing the results. I bought 100 scratch cards (stopping when I qualified for the SEC and Joker cards) and according to my account history had the following results
48 10 credit wins
4 50 credit wins
1 100 credit wins
There were also 43 1 credit bonuses some of which would have been won at the same time as a main win and others all by themselves. I did not win any free cards as I already owned them all - I believe that any that I would have won were replaced by a 10 credit win (as was the case with the previous scratch card game).
While based only on a sample of 100 scratch cards that suggests to me that the probability of winning something (to the extent of at least nominally getting your money back) on any
single scratch card is roughly 50% (plus or minus about 10%) and that the secondary Bonuses have a similar probability of being won,