I would suggest it dates from around 1989 from the version of the DR DOS
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This instruction manual is for DR DOS by digital research for PC computers(version 3.4) Details - published 1989 third edition..1146-2074-003
Known versions are DR DOS 3.31 (BDOS 6.0, 1988-06, OEM only), 3.32 (BDOS 6.0, 1988-08-17, OEM only), 3.33 (BDOS 6.0, 1988-09-01, OEM only), 3.34 (OEM only), 3.35 (BDOS 6.0, 1988-10-21, OEM only), 3.40, 3.41 (BDOS 6.3, 1989-06, OEM and retail). Like MS-DOS, most of them were produced in several flavors for different hardware. While most OEMs kept the DR DOS name designation, one OEM version is known to be called EZ-DOS 3.41.
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I doubt many were made so quite a find.
My guess is that it predates the Amiga 1200 and is more likely to be in the Amiga 500 era.