When a row in your file carries an Asset ID that an asset in the return already has, DepreciationPro treats them as the same asset and asks what to do. You can update the existing asset with the file's values, skip the row, or change the row's ID if it is actually a different asset.
This is how a register that lives in two files becomes one set of assets: import the book depreciation schedule first, then the tax schedule that uses the same Asset IDs, and update the matches. Each asset ends up carrying both sides.
What you see on the preview
A banner above the preview grid counts the matches: "5 rows match existing assets by Asset ID". It carries two bulk actions:
Update all sets every matched row to update its existing asset.
Skip all leaves every existing asset untouched. Skipping is the default, so doing nothing imports no duplicates.
Each matched row also gets its own Update / Skip toggle in the grid, so you can update all and pull individual rows back out, or skip all and update a handful.
If a matched row is really a different asset that happens to reuse the number, edit its Asset ID right in the grid. The match clears as soon as the ID no longer collides, and the row imports as a new asset.
What "update" writes, and what it never touches
The file's values only overwrite the side of the asset the file is about:
A tax depreciation file updates the asset's tax depreciation: method, convention, recovery period, elections, prior depreciation. It does not touch book depreciation.
A book depreciation file updates the asset's book (GAAP) depreciation and leaves every tax field alone.
A file carrying both updates both.
DepreciationPro reads which kind of file it is from your answer to "what kind of schedule is it" on the upload step, or detects it from the columns if you left that on the default. See Import a book depreciation schedule. The update controls say which side applies, for example "Update the existing asset with this file's values (tax depreciation only)".
The asset's identity fields are never overwritten by an update: the description, placed-in-service date, and original cost you already have stay as they are. If the file disagrees on cost or in-service date, the import completes and the summary tells you: "2 updated assets had different values in the file (cost or in-service date); the existing values were kept." Review those assets and edit them by hand if the file was right.
The result
The confirmation and the summary after the import say what happened in three counts: assets imported as new, matching assets updated, and duplicates skipped. Updated assets record the change in their history, so you can see which fields the import changed and when.
The two-file workflow, start to finish
Import the first file, for example the book schedule, with its Asset ID column mapped. The assets are created.
Import the second file, the tax schedule using the same IDs, into the same return.
The preview flags every row as a match. Click Update all.
Confirm. The existing assets now carry the tax values from the second file, with their book depreciation intact.
The order does not matter. A tax file first and a book file second works the same way, with each file updating only its own side.
Rows the update option does not cover
Description matches. A row can also be flagged as a possible duplicate because its description, cost, and date resemble an existing asset. Those rows can only be skipped or imported, not merged, because a resemblance is not an identity. Only an Asset ID match offers Update.
Multi-state grouped imports. When rows group into one asset across states, a matched group is skipped rather than updated, and the row says so.