What's actually going on
Sample boards, stain chips, cabinet doors. A spreadsheet holds who has them perfectly well: a name, a date, a phone number.
What it can't do on its own is tell you when one is late. There's no column for when the thing should come back, so there's nothing to check against today's date.
That's two jobs, not one. Recording who has what is the job a spreadsheet is good at. Being reminded when something is overdue needs a rule that compares two dates.
Most sheets are missing the second half. So people decide the whole sheet has failed, when it's one column short. This is fixable where it sits, with no new software and no barcode system.
Barcodes and QR codes solve a different problem: faster data entry when items move a lot. They don't create the reminder either. Something still has to check the due date and flag it.
The smallest fix you can do today
Add three columns to what you already have: date out, due back, and returned.
Set due back as a formula: date out plus however many days you're comfortable lending for. Leave returned blank until the item comes back, then mark it.
Then add the rule that does the checking for you. In Excel that's a conditional formatting rule built from a formula. Microsoft's own instructions say to click "Use a formula to determine which cells to format." Enter a formula that must return TRUE or FALSE. For example, compare the due-back date to today's date and check the returned column is empty (Microsoft Support).
Anything overdue turns a colour. Open the sheet, scan for the colour, done. No manual date-checking.
When it's worth keeping, cleaning, connecting, or converting
Keep the spreadsheet if you're checking it once a week and a colour-coded overdue list is genuinely enough. For three designers and the occasional homeowner loan, that's probably still true.
Clean it if the due-back column and the flag above aren't there yet. That's a data and formula fix, not a new tool, and it's usually a half-hour job.
Connect it if you want the flag to reach you without opening the sheet. A scheduled export or a calendar reminder pulling from the overdue list means you don't have to remember to look.
Convert to dedicated loan or asset-tracking software only once the sheet itself is genuinely the limit. That's when items move so often that manual entry can't keep up, barcode or not. Or when several people need to check items in and out at once without overwriting each other. Buying software before adding the due-back date just buys you the same gap with a monthly fee attached.
What "done" looks like
Done is one glance on a Monday. Everything overdue is already a colour, and you checked nothing by hand.
You'd know it's working when the "someone's had this for ages" conversations stop, because the sheet is catching that instead of your memory.
If items are usually out for weeks, a weekly look is enough. If they're out for a day or two, the flag needs to reach you sooner than that. That's the point where connecting the reminder, rather than just adding it, starts to matter.
The samples were never really the thing you were tracking. The date was.