Same type, same attribute list: nothing lost.
Different type name (or the same name, source-schema attrs trimmed/padded), every source attribute has a same-named home in the target.
Reconciled with SOME loss. Usually at least one source attribute has no
home in the target schema's shape for this type (see
droppedAttributes) — but a same-named type whose attribute lists are
reordered rather than appended/removed (neither a strict prefix of the
other, and not in BY_NAME_ATTR_REMAP_TYPES) is also lossy with an
EMPTY droppedAttributes: every name still exists in the target, but
convertRecord leaves the positional values untouched under the new
shape, so they land in the wrong slots rather than disappearing.
No representation at all in the target schema. The type IS an IfcRoot subtype, so every instance becomes a generic IFCPROXY: its own semantic type, GlobalId and every attribute are gone.
No representation at all, and NOT an IfcRoot subtype (a resource type or representation item referenced positionally by other entities). Cannot become a proxy (an IfcProduct is not a valid substitute) and cannot be dropped (referencing entities would dangle) — converting a record of this type throws.
How one entity TYPE's data survives a schema conversion.