Thanks for correcting,
this Shinagawa was modified by 1963 Residential Addressing System Labeling Implementation, and was supposedly there as label for marking purposes.
probably left unclarified since initial mapping.
we can confirm from [here](https://ja.wikipedia.org/wiki/品川区の町名#旧品川区の町名) that it was quarter(大字) in the town of Shinagawa.
you may consider using historic=district to indicate that it was quarter for historical reasons. (however not recommended)
Thanks for reading.