How to completely save the WhatsApp chat history in an Android phone

To record an important (group) chat history from WhatsApp in an Android phone, I turned to the Internet for help – but I still can not save / save the entire conversation / discussion from the beginning.
For information, my example is a group chat with a story composed perhaps of a few hundred text messages (from 2017), containing maybe thirty images, some videos and some voice files. It should certainly not exceed the limits of the WhatsApp system. There is nothing rude in the cat but a strong feeling is expressed by some, in no case should censorship be the cause.
So why on earth I can not save the full history of the cat ???
I can see the whole chat (from the beginning to the present) on my phone, but when I export the chat by email and Gmail only appears for approx. a month of cat !!!
Why? What limits and prevents to see (export?) The complete history of the cat?
I'm using the internet-recommended procedure, including the forum, in which I write. I use the following selections: More, Export chat, Include media, Send chat via (and each time, click Email or Gmail), type in the To field, then send …. it sends but by checking the mail sent, can only see the recent discussions.
Can any one advise? Your help would be appreciated.