The lead-time range is usually a lie
When a vendor lists '10-14 weeks' that's the best case. Custom finishes, COM approvals, and supply-chain hiccups all push it out. Assume actual delivery is the top of the range plus 20%. For a 10-14 week quote, plan for 17 weeks.
Stock vs. custom vs. COM
In-stock pieces ship in days. Standard catalog items with vendor-stocked fabric take 6-10 weeks. Customer's-own-material (COM) adds at least four weeks to whatever the base lead time is because the vendor has to receive, inspect, approve, and schedule the fabric. Custom finishes on case goods can double the lead time.
Build your install date backwards
Pick the install date, subtract 3 weeks for freight and assembly, subtract 2 weeks for buffer, and that's the date by which every piece needs to ship. Then filter all spec candidates against that date. It's the single most effective way to prevent lead-time failures.
Which vendors hit their dates
In general: Hooker, Universal, Norwalk, and Surya are reliable on dates. Custom upholstery houses (Hickory Chair, Wesley Hall, Hancock & Moore) are reliable on quality but slip more often on dates. Plan accordingly.