Indian and Sri Lankan letter codes
OP, FOP, TGFOP, FTGFOP, SFTGFOP — the letters accumulate and describe leaf size, wholeness and the proportion of golden tips. FTGFOP means finest tippy golden flowery orange pekoe, which sounds like a quality verdict and is a description of appearance. Below these sit broken, fannings and dust grades, which are smaller leaf destined for bags. A high grade tells you the leaf is large and tippy. It does not tell you the tea is good.
Chinese white tea grades
A picking ladder rather than a quality ladder: Silver Needle is buds only, White Peony is bud with one or two leaves, Gong Mei and Shou Mei are progressively more mature leaf. The interesting part is that it inverts for ageing — mature leaf carries more of what ageing acts on, so the cheapest grade is the one worth keeping. Buyers routinely age the expensive grade and drink the cheap one, which is backwards.
Japanese and Korean conventions
Japan grades largely by product type and harvest — shincha, ichibancha, nibancha — rather than by leaf appearance, plus steaming depth as a style descriptor. Korea grades purely by picking date: ujeon before the spring rains, then sejak, jungjak and daejak. Neither system uses the letter codes, and applying Indian expectations to them produces nonsense.
Chinese green tea and the pre-Qingming premium
The most significant Chinese quality signal is date rather than a grade: tea picked before the Qingming festival in early April commands a large premium because winter dormancy concentrates amino acids. It is a real distinction and heavily gamed — early-budding cultivars like Wu Niu Zao reach market first and are shaped to look like Longjing.
What to do with all this
Use grades to understand what you are being sold, not to rank it. A high grade narrows the range of what the tea can be; it does not place it within that range. Origin, harvest year, cultivar and processing detail are all better predictors, and a seller who supplies those is telling you more than one who supplies four extra letters.