Can anyone tell me if this is correctly constructed, with regards to the use of the expression 'it's been long since...' ? I'm trying to say that something stopped being what we think it is sometime ago. In other words our current understanding of how it works was valid until a point in time in the past, but is no longer now.

It's been long since the 'eeee' part (first 4 digits) of the batch id ceased coding the true emulsion number.

And sorry for the boring technical jargon here...
Thanks a bunch.
Yes, it's constructed correctly-- it's equivalent to it's been a long time since. However, the phrase is a bit lyrical for a technical treatise.
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'Mercy buckets' doctor Micawber. So you've noticed I was trying to practice my best english on a vulgar technical document...Emotion: geeked
Dear sirs,

Perhaps we may say «It is a long time since the 'eeee' part (first 4 digits) of the batch id coded the true emulsion number».

Kind regards, Emotion: smile