The use of the 'since' time phrase

Hi. I tried to get some help with thread I started named "Check these sentences, please" but didn't get help. Then I thought it would be better if I made sentences fit a specific topic like "the use of the 'since' time phrase" and here they are. Please help. Do you think the following sentences with the 'since' time phrases are correct?

The following one is what I wrote it the said thread (named "Check these sentences, please") (Let us assume that the letters "XX" represent the last two digits of years like 1980 or 1990.):

For this one, the harmful effect from the substance used since the early 19XXs, is causing long-term ramifications.

Now, are these correct? (Let us also assume that the letters "XX" represent the last two digits of years like 1980 or 1990.)

In operation since 19XXs, it is making big impressions on the retail market these days.

Making tools since 19XXs, they are now one of the best-known restaurant chains in the nation.