Edith Heath Ceramics Rose Peacock Luncheon Plates Lot 3

Three gorgeous vintage Heath Ceramics 9 3/8" diameter luncheon plates in the pretty Rose Peacock pattern. Two have the Heath stamp on underside center, very faded or didn't take completely, and the third plate has no stamp. All have handwritten incised mark that is hard to read but looks like "53 + 1T + La" -- I wonder if this could be the formula for an experimental glaze used on this plate? I don't know much about Heath pottery. One plate has a small shallow glaze flake just under the rim as shown -- it's about 1/4" x 1/4". The large white mark shown in the first photo is just glare, not damage, and I see only a few light utensil marks otherwise. The last two plates shown have no issues, nice vintage condition!