Table Statistics

Hello

I have three questions

1)

When I am importing schema with version 102.0.2, getting warning (gues it while exporting it does exports defnition along with the statistics)

'exporting questionable statastics',

Can you make me clear on this

2) I have a table count 25923076 rows, when I check the table statistics like num_rows, empty_blocks, blocks all are null,

     cant it be updated automatically without analyze table <table_name> compute statistics and when does the oracle analyzes the table

3) the above same table altered with a new column of datatype number and updated with a sequence,

after analyzed the table , the size of the table is same as the before, so how does this data gets inserted in the same blocks