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Text to go in the release notes:
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MARC modification templates now correctly preserve existing values when moving subfields within repeatable fields. Previously, moving subfields could cause data loss or duplication when the source subfield didn't exist in all instances of the repeatable field.
**The problem:**
When using a MARC modification template to move a subfield within a repeatable field (for example, moving 020$z to 020$a), if some 020 fields had existing $a values but no $z values, those existing $a values would be overwritten or lost.
**Example scenario:**
Given multiple 020 fields:
- 020$a with existing ISBN
- 020$a with another existing ISBN
- 020$z with cancelled ISBN (to be moved to $a)
- 020$z with another cancelled ISBN (to be moved to $a)
Previously, when moving 020$z to 020$a, the first two existing 020$a values would be replaced with values from the 020$z fields, causing data loss.
**What's fixed:**
- Existing subfield values in fields that don't contain the source subfield are now preserved
- Source subfield values are only moved to the corresponding target positions in fields that actually contain the source subfield
- The move operation correctly removes the source subfields after copying their values
- Field order and other subfields are maintained correctly
**For cataloguers:**
MARC modification template "move" operations now work reliably with repeatable fields. When moving subfields, only the fields that contain the source subfield will be affected, and all other existing values in the repeatable fields will be preserved.
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