DeliveryTimeSettings or <a class="localLink" href=https://schema.org/"/ShippingRateSettings">ShippingRateSettings are intended to apply to all <a class="localLink" href=https://schema.org/"/OfferShippingDetails">OfferShippingDetails published by the same merchant, when referenced by a <a class="localLink" href=https://schema.org/"/shippingSettingsLink">shippingSettingsLink in those settings. It is not meaningful to use a 'true' value for this property alongside a transitTimeLabel (for <a class="localLink" href=https://schema.org/"/DeliveryTimeSettings">DeliveryTimeSettings) or shippingLabel (for <a class="localLink" href=https://schema.org/"/ShippingRateSettings">ShippingRateSettings), since this property is for use with unlabelled settings." />
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isUnlabelledFallback

A Schema.org Property
Thing > Property :: isUnlabelledFallback
This can be marked 'true' to indicate that some published DeliveryTimeSettings or ShippingRateSettings are intended to apply to all OfferShippingDetails published by the same merchant, when referenced by a shippingSettingsLink in those settings. It is not meaningful to use a 'true' value for this property alongside a transitTimeLabel (for DeliveryTimeSettings) or shippingLabel (for ShippingRateSettings), since this property is for use with unlabelled settings.

Values expected to be one of these types

Used on these types

Source

https://github.com/schemaorg/schemaorg/issues/2506