Estimation Method of "how many people are there for the Chinese Expeditionary Force ?"

A netizen posted a question: "How many Chinese Expeditionary Force soldiers are still healthy? "

Accurate data statistics are difficult, but can be roughly estimated (It seems a bit disrespectful to take a heavy number of people for mathematical statistics .).My initial estimation method is:

The proportion of people over 90 years of age in Jiangsu is about 0.14% (11/7676), and the number of people over 90 years of age in mainland China is about 2 million, it is not "unable to collect statistics". No one may make statistics, but it may be a fact that all the data is changing rapidly.
In addition, you can use the followingAlgorithmTo estimate the number of remaining persons:
1. According to Baidu encyclopedia, "China has invested a total of 0.4 million people and nearly 0.2 million casualties ." Suppose there are still 0.2 million people;
2. Let us assume that they are all over 90 years old.
3. Based on the current proportion of people over 90 years old, we can roughly estimate the ratio of people over 90 years old, that is, 0.14%.
0.2 million * 0.0014 is about 300 people.
In fact, it should be far less than 300 people. Because the liberation war has killed a large number of people, not to mention the fact that they are soldiers ......

However, I thought about it later. If they don't have enough chance, they might not have more than 0.14 people who have lived for 90 years, but it should be calculated as follows:
The country's population is 1.3 billion, multiplied by 0.0014, which is 2 million. Then we should use 2 million to divide the population by 0.4 billion before liberation to assess their ratio of living over 90 years old.

That is, the proportion should be 0.0014*13/4 = 0.00455

Therefore, the estimated number of people is: 0.2 million * 0.0045, about 1000.
In fact, it should be far less than 300 people. Because the liberation war has killed a large number of people, not to mention the fact that they are soldiers ......

So,What is a more scientific estimation method??