Can we know the block height from which the ring signatures were implemented. Because i read few blocks which are pre-ring signature blocks where I see there are ring members repeating for a single transaction.
Ring CT was implemented in block #1220516 in January 2017. After September 2017, this feature became mandatory for all transactions on the network.
It's worth noting that RingCT is an improvement which added the Confidential Transactions part to the transaction format. Ring signatures existed before RingCT was implemented.