i think every bitcoin software whether its SPV, SW, LN or core all check every transaction before saving to file or relaying.
SPV doesn't check signatures.
relying on someone else to do checks, to trust them when they say everything is ok, and only double check when they say is wrong seems a little backwards
That's actually how a good share of the ecosystem presently operates. What did you think everyone runs a full node?
It seems to me there are fundamentals holes in your understanding that prevent you from making any progress in your comprehension of SW.
as i said, i insinuated SPV SHOULD... not does
but anyways,
ive got a full node. and i also have my own lite wallet. and guess what even though my lite wallet doesnt store the blockchain. i still know basic code get it to connect to other nodes and grab that specific blockchain data as and when needed.. id never ever ever blindly trust a unconfirmed tx based purely on how it was presented to me.. i always check txdata against other nodes history.. never would i ever just accept it and pass it on because it said op_check="im legit".
as i said im all for blockheight and txindex to be included in new transactions as it would make things far far easier to check.. but never should anyone just receive a tx and accept it on face value.
and now im more shocked that, with knowing how simple it is to make a lite wallet. why these other spv wallets are being so lazy.. its not rocket science.
businesses should not be running crappy lite versions..
if a business trains their cashiers on how to check if a bank note is counterfeit then the same should be true to bitcoin businesses using any wallet
they should all atleast be running some sort of lite client that checks history.. and that can be done without even needing to store said 7 years data.