Not sure what I have on my deck

I purchased this house as a foreclosure about 2 years ago. This deck wasn't in great shape then so it has been a while since it has been stained. I am not sure what is on the deck now, but in the basement I found two 5 gallon containers. One was Olympic Maximum Waterproofing Sealant Penetrating Oil Formula Toner "Honey Gold". The other was Thompson's Wood Protector Cear One-Coat coverage. Also, I tried rubbing denatured alcohol on the surface and nothing came off so I assume it is oil based. I have also included a pic of the deck surface.

I purchased a sodium hydroxide based stripper on the hand rail. I applied it with a brush, scrubbed it with a stiff bristled brush and then let it sit for 15 minutes. When I hosed it off nothing much came off. However the stain felt soft and I could dick my fingernail in it easily. I then used a pressure washer and it didn't do much better. I think tried it again and didn't get much off. When scrubbing it some comes off (balls up) but the washing gets almost nothing off. I then decided to just use the pressure washer only on the floor of the deck and it seems to be getting it mostly off. My questions are 1) what other options to I have for stripping and 2) how can I be sure if the pressure washer is getting all of the stain off..or enough of it for me to re-stain with TWP? Thanks for any help.