What it is
Sell-in is what an account orders from you: the lines on the account's book, at the account's own price, with a ship window and a cancel date. Sell-out is what that account then sold to shoppers, by door and by week, from the account's own report. They are the same styles seen from the two ends of the shelf, and Tightly keeps them married rather than added together: for each account one side or the other drives its demand, and the word under the demand figure says which.
An unreported week is absent, never zero. When an account's file has no row for a week, Tightly does not know whether nothing sold or nothing was sent, and it refuses to guess.
How Tightly decides it
Sell-in arrives through Record a booking on the account and through Order intake: an upload, an order by email, over EDI, or on Pro from the buyer portal. Sell-out arrives as the account's own file, landed on Sell-out intake; a week that came in by email says so.
Before an account's first import Tightly records how its files read, once. Sell-out intake asks it after a file's preview: Week ends on, Locations, Currency, Prices and A missing row means. The Your accounts step of Setup asks the same thing before any file has come, in a drawer titled How their sell-out reads: Their reports cover (Each store, Their distribution centres, The whole account), Their prices are in, Their prices are (Including tax, Before tax, Not known), Their file lists (Every product, every week, or Only products that moved) and Their week ends on. Its line before the button reads:
Every file from {account} is read this way until you change it. Nothing is sent to them.
The last answer is why the unreported week is a rule and not a default: one account lists every product every week and writes a zero for one that did not sell, another lists only products that moved, and no default is right for both. An import for an account with nothing recorded is refused, and the account is always chosen by a person, never read from the file.
Once a file lands and writes rows, the baseline engine grades that account's styles again from its own sell-out, and no other account's, and its coverage moves from Never reported or Gone quiet to Reporting.
The words on the face
On Sell-out intake an account is Reporting, Gone quiet or Never reported; a week with no track is a week not reported, and its hover reads "Not reported, not a zero."; Last reported is a date or Never. A declaration reads back in the words recorded: the file covers individual stores, distribution centres, not stores, or the whole account, with no store breakdown; prices are including tax, before tax, or tax treatment unknown; and every product is listed, every week, or only products that moved are listed.
Under a demand figure on the account's Book, sell-out means a predecessor of the style, as this account reported it, measured it, and sell-in means the account has reported nothing the engine can use and the brand has no level either, so its orders are the evidence; borrowed and from the brand name the other two sources. On Accounts, where an active Commitment declares the season, the word under Demand is sell-out where the account's sell-out measures that season and sell-in where it does not.
On the account's Sell-out tab one line reads what the window measured, "{account} sold {n} of {m} held in {weeks} weeks.", with "; {r} of {d} doors report" before the full stop where more than one door is on file; "{account} sold {n} in {weeks} weeks, with no shelf count." where only sales came; or, with nothing reported, "{account} reported no sell-out in {weeks} weeks."
What you can do about it
Chase the file: on Sell-out intake the row menu's Chase the sell-out file opens a note in your own mail naming the missing weeks, and on the account's Sell-out tab the same button opens Sell-out intake with that account chosen. Land it with Import a file. Where an account will never report, read its book as sell-in: record its orders as they come and the demand figure stands on them. Where the brand has its own level for a style, that row reads from the brand instead.
In the retailer chair there is no sell-out: your own tills are Sales, and Sell-out intake is not on the rail.
Glossary line
Sell-in is what an account orders from you; sell-out is what the account sold to shoppers, by door and week; an unreported week is absent on every face, never a zero.