Got something like that in practice with backup recovery - IRL most probably the sequence of events leading to that discrepancy was different (not clear yet).

```sql
drop table enum_alter_issue;
create table enum_alter_issue (a Enum8('one' = 1, 'two' = 2)) engine = ReplicatedMergeTree('/clickhouse/tables/enum_alter_issue', 'test') ORDER BY a;

-- backup / move part aside or similar operation 
insert into enum_alter_issue values ('one'), ('two');
alter table enum_alter_issue detach partition id 'all';

-- schema evolution (enum get extended)
alter table enum_alter_issue modify column a Enum8('one' = 1, 'two' = 2, 'three' = 3);
insert into enum_alter_issue values ('one'), ('two');
alter table enum_alter_issue detach partition id 'all';

-- attempt to attach back all the parts (new generation and old generation)
alter table enum_alter_issue attach partition id 'all';

Received exception from server (version 21.9.1):
Code: 53. DB::Exception: Received from localhost:9000. DB::Exception: Type mismatch for column a. Column has type Enum8('one' = 1, 'two' = 2, 'three' = 3), got type Enum8('one' = 1, 'two' = 2). 
```
: columns(other.columns)
    , secondary_indices(other.secondary_indices)
    , constraints(other.constraints)
    , projections(other.projections.clone())
    , partition_key(other.partition_key)
    , primary_key(other.primary_key)
    , sorting_key(other.sorting_key)
    , sampling_key(other.sampling_key)
    , column_ttls_by_name(other.column_ttls_by_name)
    , table_ttl(other.table_ttl)
    , settings_changes(other.settings_changes ? other.settings_changes->clone() : nullptr)
    , select(other.select)
    , comment(other.comment)
{
}
StorageInMemoryMetadata & StorageInMemoryMetadata::operator=(const StorageInMemoryMetadata & other)