To the contrary: not putting moment A in week 1 seem incredibly odd, since you did use the drugs during a week, and not putting it in week 1 would essentially make it part of a "week 0".
The way I see it the first use of drugs isn't part of any week - it is one instance of druguse that initiates the whole Addiction Test clock.
Let's look at it another way. If what you say is true a character who has used drugs on day 1 of that week could use the same drug for every other day that week, without any penalty or effect on the Addiction Threshold. He would still count as 'having used in week 1'.
In my example, if the guy used Kamikaze once but then stayed clean the rest of the week, he would still risk the Addiction check at the end of the two weeks, but at least his chances have improved slightly for not using
again after that first time.
By the way, I really like the idea of just using minor addicitons like smoking and soykaf just for roleplay purposes without involving the Addicition quality.
And I too would love to see some characters play out something like the gambling addiction, have to think about how to do that some more..