Are temporary BZA grants legal?
A BZA grant was given in 1980 for three years. I am told that Michigan ruled shortly thereafter that all temporary grants were deemed permanent and the grantee did not have to come back to the BZA for a renewal. Can you verify this?
There is no such thing as a "BZA grant". In answering this question I am assuming you are asking about a variance issued by the zoning board of appeals (ZBA). (ZBA also hears cases on ordinance interpretation, and appeals of administrative decisions, and possibly other matters.)
In Michigan when a variance is issued it travels with the parcel of land (not the owner), and is permanent. This has been the case long before 1980.
There are instances where a variance might be proposed, but the offer to have the variance has an expiration date (that is, if the owner does not actually build whatever was being proposed, the variance is not actually issued). This is so the case might be re-heard in case the zoning, or facts about the particular parcel has changed during the lapsed time. However if a variance was proposed, but not acted on, zoning has not changed, and the parcel has not changed, then there would not be any reason for a decision about a variance to be any different than what happened the first time it was asked for. So even in these types of cases, what was approved as a variance would still be the case -- so for all practical purposes the variance would stand.
You will want to confirm the 1980 variance was actually issued (not just pending).