I could be totally wrong on this, but by my recollection, it was always a legal requirement (for reasons I don’t understand) that’s sparkling wine producers label the carbonation method on the bottles. Thus, bulk sparklies are labeled “Charmat method, secondary fermentation prior to bottling,“ which isn’t something you would voluntarily put on the bottle, I don’t think.
However, by chance I was glancing at the labels of a couple of inexpensive California sparklers, and found no indication of carbonation method anywhere, front or back.
Am I wrong? What is this/is this a legal requirement?
The only regulations are for any carbonation that is a fermentation byproduct (sparkling wine) or forced carbonation (carbonated wine). The sparkling wine can be charmat or bottle conditioned, though.
https://www.ttb.gov/wine/bam/c5-class-and-type-designation.pdf