Wiktionary:About Old Novgorodian

Spelling
Prevailing spellings (> 70±5%):
 * /ѥ/: е (before 1260±25), є/ѥ (after 1350±20)
 * /ꙗ/: ѧ (before 1375±15), ꙗ (peak < 50%)
 * /у/: оу (before 1160±10), у (after 1395±15), ꙋ(peak < 35%), ѫ(rare), уо(very rare), &#1145;(...)
 * Position 1: оу(before 1155±5), у(peak < 60%)
 * Position 2: оу(before 1175±5), у(after 1335±5)