i recently realised i had still saved a seed from an airdrop address, to cut a long story short i opened the account for the first time in may 2018, the address then showed an additional 700+ decred being mined even though the balance is the same, i ask this as i was helped to retrieve the poorly written seed from a third party however would it be normal for me have mined these coins as the wallet was not accessed till then.
what i mean to say is the airdrop holders received 282 which i hold but are these 700+ additionally mined coins to be expected?
No, this is (pleasantly) strange. If you did no mining and no staking since airdrop it should be 282. I suggest analyzing your transaction history (dates, amounts) to figure it out.
here is the address the date in may is the date we cracked the seed https://mainnet.decred.org/address/DskoJYacivZcnbPvAJkwa9pU7k1q1U27Hdf
I don't see any extra coins mined to that address. It received 282.63795424 DCR in 2016. Then the funds were drained in 5 transactions: 2, 70, 3, 1, and remaining 206.63693024 DCR. Perhaps you were confused by block explorers that show some "total amount" of transaction instead of how many funds arrived at/left the address. What did look strange in that address (beyond the 5 txs, which I assume you are aware of), is that after each tx the change returned to this same address. This is strange because normally wallet generates new change addresses for every tx, so this address would be empty after the very first tx.