Three strict thresholds
The official conditions are strict: over 300 accessories, more than 5,000 gold, more than 50 m of trim. Community write-ups often quote the round numbers as the target; the first-party text is what this page follows. Exactly 300, exactly 5,000 or exactly 50 m does not meet that wording. Keep a tally while working, then confirm the unlocked achievement in Steam.
Plan one expensive dress
Set aside the accessories, trim and budget before starting a deliberate build. You can try these goals on the same dress, but do not assume that satisfying one unlocks the other two. The achievements guide recommends holding Shift to place accessories continuously, with gemstones as its example. Record how many items you place in each batch and how much trim you use; inventory changes can help check that tally.
Over 300 accessories
301 is the simplest whole-number target above 300. Use Shift for continuous placement and work in counted batches, such as ten batches of 30 followed by one extra item. Count items actually left on the dress, allowing for anything you remove. The community guide uses gemstones; it does not establish that every accessory type contributes identically. Your placement tally and inventory consumption help you keep track, but Steam's achievement state confirms whether the game awarded it. Exactly 300 is below the official “over 300” condition.
Over 5,000 gold
The official text says more than 5,000 gold on a successful dress; the achievements guide reports it triggering on commission and off-rack dresses alike. Keep a spending tally for the materials used on that dress, with room above 5,000, and complete it successfully. The exact counting formula is not documented, including whether unused purchases contribute, so buying expensive stock alone is not a confirmed route. If using a commission, satisfy its own requirements as well.
Over 50 m of trim
50 m = 5,000 cm, and the achievement needs more than that on one dress. Place the trim on the dress rather than only buying it. Record stock length before and after your placement batches, account for removed trim, and keep working past the threshold. A commission's small Trim or Lace Trim requirement is a separate check: the pictured Gala Supporter draft has Trim 246/20, or 246 cm against 20 cm, so its 2.46 m is still far below 50 m.
Finish the dress and check each achievement in Steam. If one did not unlock, return to its own condition: more than 300 placed accessories, more than 5,000 gold with a successful result, or more than 50 m actually used. Do not infer all three from green commission rows.