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). 
```
{
    if (&other == this)
        return *this;
    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;
    if (other.settings_changes)
        settings_changes = other.settings_changes->clone();
    else
        settings_changes.reset();
    select = other.select;
    comment = other.comment;
    return *this;
}
void StorageInMemoryMetadata::setComment(const String & comment_)