Unless this is a technical term I don't know about, launch is used for the moment when a product goes on the market and is effectively launched by the manufacturer. Otherwise spacecraft are launched into space. Hard to tell without knowing what kind of device.
since then in that sentence is awkward as hell, if not downright incorrect.
I would use thereafter or from thereon in or from that point forward (in order of personal preference).
There's a lot of confusion around this, and a lot of half-true "rules" are taught.
The actual rule for the present perfect is fairly simple. The present perfect is a present tense, designating a present situation, so it cannot be used with a temporal expression which does not include the present, the moment at which the sentence is uttered.
Consequently:
okThe directors have met is acceptable, because there is no temporal modifier. This merely asserts that the consequences of the fact of their meeting (whatever those consequences are) are now in play.
okThe directors have met this week is acceptable, because the temporal modifier this week designates a timespan which includes the present: it runs from the beginning of the current week right up to the moment of speaking.
∗ The directors have met last week is not acceptable, because the temporal expression last week designates a timespan which lies entirely in the past, ending with the beginning of the current week.
Note, however, that an entirely past temporal expression may be included in a present perfect sentence if it is 'bracketed' with commas or dashes or parentheses; it is then understood as a 'supplement', not integrated into the sentence but added to the sentence as an afterthought.
okThe directors have met—just last week, as a matter of fact.
ADDED:
DamkerngT points out that you conclude that use of simple past with an indefinite temporal expression is incorrect. This is not the case. The simple past can be used with no temporal or with indefinite temporals:
okThe directors met.
okThe directors met sometime.
okThe directors met before lunch.
okThe directors met after that.
The only sort of temporal which cannot be used with the simple past is one which cannot be interpreted as lying entirely in the past, such as now or currently or tomorrow.
Best Answer
Since in this context means after (i.e. - after some time explicitly or implicitly identified in supporting text). It might help OP to imagine replacing since with after the time at which in both his examples.
In other contexts, since can mean because, but that's really just a metaphoric extension of the above.
I think what's bothering OP is that since has many subtly different usages. Here are just a few from OED:
Most (but not all) senses imply continuity from whatever time in the past is indicated by since, up to now. For example, "I have known John since we were children" is a very common context, and we normally use past perfect there because we still know him now.
But suppose you were at John's funeral? It would be perfectly grammatical to say "I knew John since we were children" (you don't really know him any more, since he's dead). I suspect many native speakers might have the same misgivings as OP, but I think it's just because we're more used to contexts where there is continuity into the present. FWIW, I think I might be tempted to say I knew him since when, or even since way back when, to distance myself from the standard up till now/ever since then implication.