One may have multiple forms 16 if he/ she switches job for more than 1 time in a financial year. To account for tax, you need to collect the various forms 16 from the previous employers stating your salary which will help you arrive at your annual salary earned. To substitute the process, one can calculate the total salary by adding up the amount of credited salary from the salary slips or statements. Form 16 is issued by the employer which states how much salary has been paid to the employee in a specific financial year.
Now, another concept is form 26AS which depicts the amount of TDS pertaining to one's salary. This TDS needs to be deposited with IT department by the employer and should match with individual data at micro level. You need to check if the amount paid by the employer is matching with your data in official website of IT department or not.
Every month, a portion of your salary is transferred to PF account and similarly the employer makes a specific contribution to that account. One can either choose to withdraw money from his/ her PF account or transfer it to next employer. Withdrawing PF amount up to 5 years may result in taxation of that amount. To transfer the account, form 19 and form 10C need to be filled.