I am looking for some 3rd party KYC options to use for an ICO. What are the typical companies used by successful or respected ICOs?
Also how do these companies work for KYC if the investor later changes their passport or address?
There is no such thing as a KYC provider. However your expectations to outsource compliance are hard to meet. There are businesses that can help you with this, but there are no business that can do 100% this for you... if somebody claims they are "compliant" they most likely aren't.
Know your customer is your your own business as a customer. You need to understand your customers, if they behave what is reasonable to expect for their income level and what is their source of funds.
What you can find is a patchwork of providers that do identity verification - e.g. check uploaded id documents for you. Also you can find a patchwork of providers, like Coinfirm, which provide some level of chain analysis data for your transactions. For high value contributions, there is no magic bullet and you need to ask the investors evidence yourself what is their source of wealth.
Then, you as a business, assemble your information from these sources and have it handled and stored in a compliant manner for your local, incorporation, regulation. This includes concerns from anti money laundering regulation (up to 5 years), GDPR and such.
Nearly every ICO your identity are requested for KYC and also more often for AML because of the regulations of the authorities. Some free Airdrops asking the same.
Why do people trust that ICO token sales more as an ico where no KYC / AML is being asked? Of course you still send all your data on someone you do not know.
With that scan of your front and back of your passport or ID card, and a photo of yourself, someone can easily use your identity now on exchanges and ICOs. Especially since the scammers are now moving to new ways, the easiest way is to make purchases with your data.